Plasma sources are employed in plasma processing chambers or reactors, for example, in semiconductor device fabrication technology, for coating wafers or other semiconductor structures and other substrates. The substrates or wafers are introduced into the processing chamber by way of the entrance lock. After substrate placement in the processing chamber, a reduced pressure suitable for the ensuing coating or processing operation is generated by a vacuum pump. After the desired reduced pressure is obtained, (e.g., 0.1 to 0.2 mbar) a plasma source (e.g., a magnetron or a capacitive electrode) is activated with a high-voltage high-frequency source. The magnetron or capacitive electrode introduces high-frequency energy into the processing chamber which is filled with a suitable processing gas.
By application of the high-frequency energy to the electrode, the processing gas is ionized in the processing chamber to generate a plasma. The substrate or material to be processed, which is located in the processing chamber (also designated as the receptacle), is exposed to the plasma. During the processing operation, fresh processing gas is added to the plasma reactor continuously, and at the same time contaminated or consumed gas is drawn off.
After processing of the substrate in the processing chamber is complete, the substrate is passed to the outside by way of an exit lock, in which at first the normal ambient pressure is established. The exit lock at the same time ensures that no processing gas can get into the environment.
It is well known that in coating operations in a processing chamber, for example a vacuum chamber, the inside walls of the chamber as well as the plasma source itself are always coated as well. These coatings, according to the prior art heretofore disclosed, cannot be prevented. The result is that the productivity of such a system is limited by the parasitic (undesirable) coatings on the plasma source or other components of the processing chamber. Upon reaching a pre-assigned boundary layer thickness, these deposits must be removed.
According to the past prior art, for example, as customary in the microelectronics industry, the processing chamber is cleaned by in situ etching (e.g. plasma etching) after the parasitic coatings on the plasma source and the other components, exceed a boundary layer thickness. Alternatively, the processing chamber may of course be aerated, opened and then cleaned mechanically. A disadvantage of both methods, of course, is that the productivity of the reactor reduced since no coating can be carried out during cleaning. Further, the interruption caused by the cleaning operations negatively affects the productivity of integrated production lines.
Other disadvantages of the mechanical cleaning or etching operations relate to the deleterious generation of particles in the processing chamber and health risks to personnel cleaning the processing chamber.
Consideration is now being given to ways of improving plasma processing systems and methods. In particular, attention is directed to improving plasma reactor structures and operations. Desirable plasma reactors may have uniformly high productivity, and permit rapid, simple and selective cleaning of the plasma sources and adjoining portions of the processing chamber.